1. Field of the Invention
The present invention relates to revolution number control systems for engines, and preferably, revolution number control systems for engines having centrifugal clutches.
2. Related Art
As a revolution number control system for controlling the revolution number of an engine, there has been known, for example, Japanese Patent No. 2917057 xe2x80x9cStarting-Time Revolution Number Control Systemxe2x80x9d.
FIG. 5 of the above publication shows a graph of revolution number control by a starting-time revolution number control system which gradually increases a corrected value of the amount of fuel supplied to an internal combustion engine from a predetermined engine revolution number CVEN toward a connection engine revolution number CEN of a clutch mechanism.
In the starting-time revolution number control system above-mentioned, connection of the clutch mechanism is prevented by lowering the engine revolution number through increasingly correcting the amount of fuel. Therefore, for example, the fuel injected from a fuel injection valve adheres to and stagnates on inside walls of an intake pipe. Therefore, all the injected fuel does not immediately reach into the combustion chamber, so that combustion conditions are changed. Moreover, it is difficult to accurately control the engine revolution number.
An object of the present invention is to accurately control the engine revolution number so that the revolution number does not needlessly increase to the engine revolution number at the time of connection of a centrifugal clutch, in a revolution number control system for an engine.
In order to attain the above object, provided are a revolution number control system for an engine comprising a centrifugal clutch connected when the engine revolution number reaches a preset revolution number, and throttle opening change detecting means for detecting a change in the throttle opening of the engine. The revolution number control system comprises ignition timing delay controlling means for delaying ignition timing from the ignition timing at a first predetermined revolution number when the engine revolution number is between a first predetermined revolution number and a second predetermined revolution number, where the first predetermined revolution number is a predetermined revolution number smaller than the preset revolution number and the second predetermined revolution number is the preset revolution number. The revolution number control system controls revolution number by operating the ignition timing delay controlling means when the throttle opening change detecting means does not detect a change in the throttle opening.
With the ignition timing delay controlling means, ignition timing is delayed from the ignition timing at the first predetermined revolution number when the throttle opening change detecting means does not detect a change in throttle opening and the engine revolution number is between the first predetermined revolution number and the second predetermined revolution number. Accordingly, the engine revolution number is prevented from reaching the second predetermined revolution number, and needless connection of the centrifugal clutch is prevented.
Therefore, in comparison to the conventional system in which a rise in the engine revolution number is prevented by increasingly correcting the amount of fuel, the system of the present invention can control the engine revolution number with high accuracy without being affected by stagnation of fuel in the intake pipe or the like.
According to another principle of the present invention, the ignition timing delay controlling means increases the delay amount of ignition timing according to an increase in revolution number from the first predetermined revolution number.
The first predetermined revolution number is set, for example, in the vicinity of an idle revolution number, whereby the delay amount in the vicinity of the idle revolution number is made small, and variation of revolution is thereby restrained. In addition, the delay amount is increased as the increase in the revolution number from the first predetermined revolution number is larger, whereby the engine revolution number is swiftly lowered.
According to yet another principle of the present invention, the fuel supply amount reducing means for reducing the amount of fuel supplied to the engine at the time of delaying the ignition timing by the ignition timing delay controlling means is provided, in addition to the ignition timing delay controlling means in an engine provided with a catalyst for cleaning exhaust gas.
When the ignition timing is delayed, the temperature of exhaust gas is raised due to after-burning; however, by reducing the amount of fuel, the rise in the temperature of the exhaust gas is restrained, and the temperature of the catalyst is prevented from excessively rising. As a result, life of the catalyst can be extended.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.